linux-kernel - Re: [PATCH v5 5/5] Add ioctls to enable and disable local controls on an instrument

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Message-ID: <20151125091256.GA1665@slacky>
Date:	Wed, 25 Nov 2015 10:12:56 +0100
From:	Dave Penkler <dpenkler@...il.com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	peter.chen@...escale.com, teuniz@...il.com,
	USB <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 5/5] Add ioctls to enable and disable local controls
 on an instrument

On Sun, Nov 22, 2015 at 12:36:53PM +0200, Andy Shevchenko wrote:
> On Sun, Nov 22, 2015 at 10:51 AM, Dave Penkler <dpenkler@...il.com> wrote:
> > On Wed, Nov 18, 2015 at 11:41:30AM +0200, Andy Shevchenko wrote:
> >> On Wed, Nov 18, 2015 at 10:38 AM, Dave Penkler <dpenkler@...il.com> wrote:
> 
> 
> >> > +       if (rv < 0) {
> >> > +               dev_err(dev, "simple usb_control_msg failed %d\n", rv);
> >> > +               goto exit;
> >> > +       } else if (rv != 1) {
> >> > +               dev_warn(dev, "simple usb_control_msg returned %d\n", rv);
> >>
> >> Actually here what king of results could be? 0? 2+? In all cases of
> >> error you have to provide an error code.
> >>
> >
> > We seem to be going round in circles here, last time you suggested to
> > propagate the return value.
> 
> You didn't pay much attention to where I put my comment. You have few
> branches depending on return value
> 
> 1) negative, apparently an error code, should be propagated if nothing
> specific to framework;
> 2) zero, what does it means?

Zero bytes transferred -> error

> 3) one, seems the expected result when success, so, error code should be 0;

Which it is when we drop through

> 4) two, three, ??? non-negative numbers,see 2).
> 
> For my understanding 2) and 4) have to return what you initially had -EIO.
> 
> > The non-negative return is the number of bytes
> > transferred which should be 1 unless there is some usb implementation
> > flakiness happening. So I will go back to returning -EIO.
> 
> Yes, in *this* branch.
> 

OK so now I have the same as in v4 again:

	if (rv < 0) {
		dev_err(dev, "simple usb_control_msg failed %d\n", rv);
		goto exit;
	} else if (rv != 1) {
		dev_warn(dev, "simple usb_control_msg returned %d\n", rv);
		rv = -EIO;
		goto exit;
	}

> >
> >> > +               goto exit;
> >> > +       }
> >> > +
> >> > +       if (buffer[0] != USBTMC_STATUS_SUCCESS) {
> >> > +               dev_err(dev, "simple control status returned %x\n", buffer[0]);
> >> > +               rv = -EIO;
> >> > +               goto exit;
> >> > +       }
> >> > +       rv = 0;
> >> > +
> >> > + exit:
> >> > +       kfree(buffer);
> >> > +       return rv;
> >> > +}
> 
> -- 
> With Best Regards,
> Andy Shevchenko
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